Using honed-finish or waxed marble tiles is recommended to help give you more traction as you step.
Make sure the stairs are dry, because marble is indeed slippery when wet. Try going to Interstone Marble and Granite for your material. We take pride in carrying a large inventory of top quality stone products at great prices! You could think about putting a little carpeting for the center portion of your stairs while still showing off your marble on the sides. I also imagine that you will have a strong and sturdy handrail as well to steady you. Marble stairs add true elegance to any surface but on stairs it looks incomparable.